Endodontic therapy or root canal treatment is the treatment of choice for prevention or recovery of a tooth from infection, or where it is otherwise threatened by infection, cracking or decay, extending (into or near) to or approximating the pulp chamber.
Bacterial infection in the root canal or tooth, typically affecting the pulp material, causes a process of pulpitis, an often painful process affecting the pulp chamber or endodontic chamber and root canal structure. This results in an infection of the tooth and often results in an extending lesion beyond the apex or other canal connecting the nerve space to the adjacent soft and hard tissues of a tooth and may present as an abscess within these surrounding tissues. Infected and inflammatory bacterial fluids emanating from within the tooth structure and apical portion of the tooth escape through the apex of the root into the surrounding periodontal tissue, causing substantial inflammation, with associated tissue changes. Without intervention, the tooth will die and may require extraction and the infection may spread into the surrounding tissues causing potentially life-threatening abscesses in the head and neck region. Root canal treatment (endodontic therapy) allows treatment of such infection and the structural integrity of the tooth to be saved.
The purpose of root canal treatment is to entirely remove all tooth pulp and living tissue as well as any bacterial organism or biofilm and to seal off the root canal by filling the pulp cavity. This allows the crown portion of the tooth to be restored safely using established restorative options such as composite filing or artificial crowns, thereby retaining a non-vital tooth in structural and functional senses.
A typical procedure that dentists will undertake in a root canal treatment on a patient is to open the tooth by drilling through the crown, removal of the pulp (which comprises blood vessels, nerve tissue and soft tissue and which is typically infected in a tooth undergoing root canal treatment), cleaning and enlarging of the root canal (e.g. with an incremental series of small files) to ensure that all infected material is removed and to ensure that the root canal is large enough to be effectively filled. Where there are multiple roots, each will have to be identified, cleaned and treated. Furthermore, roots may have a complex morphology in terms of overall structure including curvature and accessory canals. Typically, removal of pulp material and enlarging of the root canals will be done at a first visit. An antibacterial (e.g. sodium hypochlorite) will typically be applied into the endodontic cavity to enhance the removal and killing of any residual microbial burden. Optionally the tooth will be temporarily filled and closed and reopened at a second visit at which point, cleaning of the endodontic cavity will be resumed. A root canal filling material will be inserted into the cavity and a well-fitted filling, such as a glass ionomer cement, and, optionally, a crown will seal the tooth and ideally prevent re-infection.
The most common cause of failure of root canal treatment, aside from poor technique (e.g. missed root canal or improperly sealed access cavity) or iatrogenic contamination, is residual bacteria in the root canal space and at the apex of the tooth, which can arise due to difficulty in visualising or accessing all aspects of the inside of the roots, particularly in the apical region, of the root canal which may harbour remaining tissue or bacteria. As a result, dental practitioners may over-prepare the canals to remove the infected dentine, at potentially unnecessary time and cost, or may underprepare leaving a substantial bio-burden within the tooth structure with concomitant risk of re-infection. In England and Wales alone, over 1,000,000 RCTs (root canal treatments) were carried out in NHS surgery in 2003 (Dental Practice Board, 2003). Yet, still, approximately 15-25% of endodontic root canal procedures fail. Therefore, these procedures often need to be repeated due to persistent infection, thus representing a significant time and cost burden, in addition to often requiring specialist intervention and dramatically reducing the prognosis of the tooth to be treated. Since it has been proven that the complete disinfection of the root canal space improves the chances of favourable outcome (80% vs 44%) of the root canal treatment, microbiological sampling of the canal content could be sued to determine the bacterial content. However, this procedure is inherently flawed as it adds several days to the procedure time (since microbial analysis in a cell culture laboratory is required) and furthermore, bacteria cultures will only identify bacteria present in the obtained sample as well as being limited to culturable material and so can result in false negatives. This leads to canals which ultimately fail as they are still infected at the time of obturation despite negative culture results.
A number of patent publications exist in the field of endodontics, bacteria eradication and imaging.
WO-A-2005/102033 describes a method of radiation ablation of residual bacterial and biofilm populations in a root canal, typically the apical portion of the root canal, which is difficult to reach with instruments and irrigation fluid. An optical probe with a head that causes lateral dispersion of the near infra-red radiation enables thermolytic eradication of bacteria and biofilm without the problems of hot-tip and other such problems experienced with previous laser ablatement methods. However, the apparatus is expensive and only effective in and insofar as the probe is inserted into the appropriate root canals. Furthermore, this device will not assess the actual presence of viable bacteria pre- or post-treatment.
WO-A-95/08962 describes a method of imaging a root canal utilising induced fluorescence imaging or induced fluorescence spectroscopy. In undertaking an endodontic treatment, dentists may obtain X-ray images of the tooth in order to establish the structure and in particular the number and shape of roots (and root canals) in the tooth. A problem with X-ray is that the apical portion of the root canal (the portion where structural complexities are likely to exist) is partially obscured in such images by the jaw bone. An apparatus comprises an elongated tool and optical fibre which carries ultraviolet and blue light to induce fluorescence within the root canal. Fluorescence is captured by the optical fibre and transmitted to a sensor which monitors return light to build an image of the root canal structure. There is no disclosure of determining the presence or absence of bacteria using the probe and further, the probe and sensor is a complex kit as is necessary to deliver sufficient radiation to excite and detect fluorescence.
There is a need for a chair-side test to determine the presence of biofilm, bacterial cells or other cells or cell debris in the endodontic space during endodontic therapy.
The present inventors have devised a method and instrument for the identification of cells, and particularly viable cells, and a method for achieving and identifying a preparation-phase treatment endpoint for use in situ in the dental clinic during endodontic therapy.